A continuing effort to more cost efficiently manufacture furniture of different kinds has led to continuous improvements in the production of spring coils. Further, there is a continuing effort to improve the quality and comfort of furniture in which spring coils are used, for example, seating cushions and mattresses. In particular, in order to support a human body in the proper posture when lying on a mattress, in many mattresses, it is desired to provide a mattress with spring coils at different locations having differing stiffness or spring constants to conform with the loading imposed by a human body.
In order to change the stiffness of a spring coil, a different diameter or gage wire is sometimes used to form the coil, for example, a thicker wire is used to make a stiffer coil and a thinner wire is used to make a less stiff coil. The tooling of known spring coiling machines is made to handle a specific wire diameter. Therefore, if it is desired to use a wire of a different diameter, the wire specific tooling of the spring coiling machine must be replaced with tooling made to handle wire of the different diameter. Obviously, the requirement of physically switching the tooling on a spring coiling machine so that it can work with a different size of wire is time consuming and expensive. Not only is there the added cost of skilled labor required to modify the spring coiling machine, but there is a significant cost in the production lost from the spring coiling machine while it is shut down for the tooling changeover. In addition, the further cost to manufacture and store different sets of wire specific tooling is also burdensome.
It is known to be able to automatically and continuously manufacture spring coils of different diameter and pitch from the same wire, thereby providing spring coils of differing stiffness or spring constants. However, the limitation of making spring coils from only a single wire severely limits the range of spring coil stiffness that can be provided. Further, the end product, for example, a mattress, is a fixed size and is normally designed to use a predetermined number of spring coils. Changing the diameter of selected spring coils to change the coil stiffness causes the number of spring coils used in the mattress to also change. Adding another variable, that is, the number of spring coils, substantially complicates the mattress design and manufacturing processes; and therefore, in the production of mattresses and other seating furniture, it is not practical to change spring coil stiffness by changing the spring coil diameter.
Consequently, there is a need for a spring coiling machine having a wire feed that permits coil springs to be automatically and continuously manufactured from different sizes of wire.